Treatment of silica

ABSTRACT

A silica-containing composition suitable for supporting chromium to produce a catalyst capable of giving high melt flow olefin polymers for such applications as injection molding and the like requiring a narrow molecular weight distribution, is produced by treating a silica-containing material at an elevated temperature with either (1), CO, (2) a bromine or iodine component, or (3) an oxygen-containing sulfur component, more specifically a carbon, oxygen and sulfur-containing component. Thereafter, anhydrous chromium can be added, for instance, by means of a hydrocarbon solution of a soluble chromium compound, and the resulting composition activated in air to produce a catalyst. The bromine or iodine treated silica contains bound bromine of iodine if the treating agent is HBr, HI, an organic halide of Br or I or elemental Br or I used in conjunction with a reducing agent. This material is a novel composition of matter and is suitable for use as a reinforcing agent in rubber or plastics and as a support for a chromatographic column in addition to be suitable for supporting a chromium compound to produce a catalyst.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of copending application Ser. No. 44,809, filedJune 1, 1979, now U.S. Pat. No. 4,248,735, which in turn is acontinuation-in-part of copending application Ser. No. 857,552, filedDec. 5, 1977, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of treated silica.

Chromium oxide catalysts on a silica-containing support can be used toprepare olefin polymers in a hydrocarbon solution to give a producthaving excellent characteristics from many standpoints. Supportedchromium oxide catalysts can also be used to prepare olefin polymers ina slurry system wherein the polymer is produced in the form of smallparticles of solid material suspended in a diluent. This process,frequently referred to as a particle-form process, has the advantage ofbeing less complex. However, certain control operations which are easilycarried out in the solution process are considerably more difficult inthe particle-form process. For instance, in a solution process, controlof the molecular weight can be effected by changing the temperature withlower molecular weight (higher melt flow) being obtained at the highertemperatures. However, in the slurry process, this technique isinherently limited since any effort to increase the melt flow to anyappreciable extent by increasing temperature would cause the polymer togo into solution and thus destroy this slurry or particle-form process.

Heretofore silica has been treated with chlorine to produce achlorinated silica but efforts to halogenate silica with bromine oriodine have not been successful.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a catalyst capable ofgiving high melt flow polymer; it is a further object of this inventionto provide a catalyst suitable for use in slurry polymerization systems;it is a further object of this invention to produce an improved supportfor chromium-containing catalysts; it is a further object of thisinvention to provide an improved method of producing achromium-containing catalyst; and it is yet a further object of thisinvention to provide a catalyst capable of giving polymer suitable forinjection molding and other applications requiring high melt flow andnarrow molecular weight distribution; it is yet a further object of thisinvention to produce a bromine- or iodine-containing silica composition;and it is yet a further object of this invention to provide a novelstable free radical composition.

In accordance with this invention, a silica-containing composition istreated at an elevated temperature with an ambient selected from (1)carbon monoxide, (2) a bromine- or iodine-containing component or (3) anoxygen-containing sulfur-containing component, more specifically acarbon, oxygen and sulfur-containing component.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings forming a part hereof, FIG. 1 is an ESR spectrum of afree radical containing silica produced in accordance with an alternateembodiment of this invention and FIG. 2 is an ESR spectrum of a knownfree radical containing reference sample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The silica-containing material to be treated can be selected fromcatalytic grade silica, silica-alumina, silica-boria, silica-titania,silica-zirconia, and the like, and mixtures thereof, in which the silicaconstitutes from 80 to 100 weight percent of the silica-containingmaterial. Suitable silica-containing materials are the catalyst supportsbroadly disclosed in Hogan et al, U.S. Pat. No. 2,825,721 (Mar. 4,1958), the disclosure of which is hereby incorporated by reference. Whenthe purpose is to produce a catalyst support the silica-containingmaterial preferably is a cogel, that is, a silica produced bycoprecipitating titanium and silica as disclosed in Dietz, U.S. Pat. No.3,887,494 (June 3, 1975), the disclosure of which is hereby incorporatedby reference. For instance, this cogel formation can be carried out byadding a titanium compound to a mineral acid, introducing an alkalimetal silicate into the acid containing said titanium compound to form ahydrogel, aging the hydrogel for a time of greater than 1 hour, washingthe thus aged hydrogel to produce a substantially alkali metal freehydrogel, forming a mixture comprising the thus washed hydrogel and anormally liquid oxygen-containing water soluble organic compound, andseparating said organic compound and water from said mixture to form axerogel. The titanium is present in these cogels in an amount within therange of 0.1 to 10, preferably 0.5 to 5 weight percent titanium based onthe weight of the dried cogel (xerogel).

The treating agents are (1) carbon monoxide, (2) a halogen componentselected from bromine or bromine-containing ambients or iodine oriodine-containing ambients and (3) an oxygen-containing sulfurcomposition preferably containing an organic sulfur compound, morespecifically a carbon, oxygen and sulfur-containing compound.

In the first embodiment utilizing carbon monoxide, the ambient can bepure carbon monoxide or carbon monoxide in admixture with an inert gassuch as nitrogen, argon, helium, etc. In such mixtures, the carbonmonoxide content usually ranges from about 1 to 90 mole percent.

In the second embodiment wherein a bromine-containing material isutilized, bromine vapor itself can be used either alone or incombination with air or CO, preferably CO. Other suitablebromine-containing materials are HBr, and organic bromides like CH₃ Brwhich can be used alone or with bromine vapor. Generally, bromine or thebromine-containing compound constitutes from 0.01 to 10 mole percent ofthe mixture where a mixture with air or CO is used, and more preferablyfrom about 0.1 to about 5 mole percent (the remainder being air or CO).Alternatively, the active ingredients (the bromine component or thebromine component plus air or CO) can constitute 1-90 mole percent ofthe ambient and the remainder can be an inert gas such as nitrogen,argon, or helium. Sufficient bromine is used during the contactingprocess whether in the form of bromine or a bromine-containing compoundsuch as HBr by regulating its concentration or length of contacting timesuch that a weight ratio of the silica-containing material such as asupport to bromine ranging from about 100:1 to about 0.5:1 is employed.

In the second embodiment where an iodine-containing material isutilized, iodine vapor itself can be used either alone or in combinationwith air or CO, preferably CO. Other suitable iodine-containingmaterials are HI and organic iodides such as CH₃ I which can be usedalone or with iodine vapor. Generally, iodine or the iodine-containingcompound constitutes from 0.01 to 10 mole percent of the mixture where amixture with air or CO is used, and more preferably from about 0.1 toabout 5 mole percent (the remainder being air or CO). Alternately, theactive ingredient (the iodine component or the iodine component plus airor CO) can constitute 1-90 mole percent of the ambient and the remaindercan be an inert gas such as nitrogen, argon or helium. Sufficient iodineis used during the contacting process whether in the form of iodine oran iodine-containing compound such as HI by regulating its concentrationor length of contacting time such that a weight ratio of thesilica-containing material such as a support to iodine ranging fromabout 100:1 to about 0.5:1 is employed.

Alternatively, an iodine or bromine solution (or in the case of bromine,liquid bromine) can be used to impregnate the silica-containingcomposition and thereafter the thus impregnated composition can betreated at the elevated temperature with CO.

This second embodiment produces a novel silica-halogen composition ofmatter definable without resort to the method of manufacture when areducing agent such as CO or hydrogen is used with the bromine or iodineor when HI or HBr, an organic bromide or an organic iodine is used. Whenthe silica-containing material is heated to an elevated temperature inCO as defined herein and contacted with Br₂ or I₂, the Br₂ or I₂ isabsorbed onto the silica. It does not come off at 1600° F. (871° C.) inCO or N₂. The reaction is postulated to be with surface silanol groupsas follows:

    .tbd.Si--OH+C0+Br.sub.2 →.tbd.SiBr+.[.Co.sub.2 .]. .Iadd.CO.sub.2 .Iaddend.+HBr or

    .tbd.Si--OH+CO+I.sub.2 →.tbd.Sil+CO.sub.2 +HI.

The composition can contain from 0.01 to 20 preferably 3 to 10 weightpercent Br or I based on the weight of silica. This can also beexpressed in terms of the millimoles of halogen per 100 square meters ofsurface area of the silica, 0.001 to 1 millimoles/100 square meters,preferably 0.03 to 0.3 millimoles/100 square meters being suitable. Thereaction product is remarkable in that bromine or iodine (which arenormally volatile at even room temperature) are held fast to the silicaeven at red heat (800°-900° C.). Even SiI₄ evaporates at 80° C. Thiscomposition can be used as a reinforcing agent for rubber and plastics,or a chromatography support or the surface bromide or iodine can beburned off and the composition is a superior support for chromium toproduce an olefin polymerization catalyst.

Further with respect to burning off the iodine or bromine, a second newcomposition of matter (a stable silica free radical) is formed when theabove silica-iodine or silica-bromide is exposed to oxygen at elevatedtemperatures (300°-800° C.). A purple gas is released (I₂) in the caseof the silica-iodide and a red gas in the case of bromine and analysisthen shows that the silica contains little or no iodide or bromine.Since oxygen is a stronger oxidizing agent than iodine or bromine, it islikely that oxide would replace iodide or bromide releasing iodine orbromine gas. But ordinary oxide is a two electron oxidizing agentwhereas iodide or bromide consumes only one electron. In solution or ingas phase, the reaction between one oxygen and two iodides is simple:

    4I.sup.- +O.sub.2 →2I.sub.2 +.[.2O.sup.50 .]. .Iadd.2O.sup.= .Iaddend.

But on a silica such a reaction is difficult because each iodide orbromide is fixed and isolated on the surface. The result is a highlynovel reaction and product. Each iodide uses less than the maximumoxidizing capacity probably as follows:

    .tbd.SiI+1/2O.sub.2 →.tbd.Si--O+1/2I.sub.2

Similarly with bromine, the equation would be

    .tbd.Br+1/2O.sub.2 →.tbd.Si--O+1/2Br.sub.2

The product is unusual in that the oxide radical O contains an unpairedelectron and is thus normally highly reactive, not existing under normalcircumstances except as short lived intermediates in explosions andother fast reactions. But bound to a silica surface, it is stabilized.The electron spin resonance spectrum set out in FIG. 1 shows anunusually powerful signal which proves the existance of stable freeradicals. Using the magnetic field at mid resonance, and the pitchreference signal set out in FIG. 2, a g value of 2.0448 can becalculated which characterizes the ESR spectra.

The details of the calculations and conditions used to arrive at a g of2.0448 for the silica-iodine sample from FIGS. 1 and 2 are as follows.

    __________________________________________________________________________    Output From ESR Data Acquisition Program                                      __________________________________________________________________________    Sample Parameters:                                                            Description         Partially oxidized silica + iodine (-196, LP) file                            MAMCG                                                     Modulation          100                                                       Gain                1000                                                      Temperature         196.0 C.                                                  Sample in           Liq. N2 Dewar                                             Derivative Maximum  .[.E Volts.]..Iadd..7569754E - 05 Volts.Iaddend.                                                          at 2436.9 Gauss.              Derivative Minimum  -.7498365E - 05 Volts       at 2847.2 Gauss.              Absorption Maximum  .386732E - 02 Volts* Gauss  at 2664.1 Gauss.              Area of Absorption  .3348080E + 01 Volts* (Gauss)**2.                         G = 2.0448                                                                    Reference Parameters:                                                         Description         Varian reference sample: G = 2.0028                       Modulation          400                                                       Gain                400                                                       Temperature         26.0 C.                                                   Sample in           Cavity                                                    Derivative Maximum  .4973989E - 04 Volts        at 3251.3 Gauss.              Derivative Minimum  -.2294782E - 04 Volts       at 3276.5 Gauss.              Absorption Maximum  .6870860E - 02 Volts* Gauss at 2721.0 Gauss.              Area of Absorption  .1862722E + 02 Volts* (Gauss)**2.                         Magnetic Field Parameters:                                                    Center field        2500.0 Gauss.                                             Scan range          5000.0 Gauss.                                             Microwave Power 15.0 DB. Attenuation.                                         Number of Points - 793                                                        __________________________________________________________________________

Of course, applicants do not wish to be bound by the theory that thespecies is .[.Si--O.]. .Iadd..tbd.Si--O.Iaddend.; it could be somethingelse such as .[.Si--O₂ .]. .Iadd..tbd.Si-O₂. .Iaddend.But the ESRspectrum proves the existence of a stable free radical and therefore aunique composition because silica or silica iodide does not produce asignal. Since radicals are highly reactive, this opens up a number ofpossibilities to use silica as a reactant.

As between iodine and bromine, iodine is preferred in producing thesilica-halogen compositions for use as a chromatography support or foruse as an intermediate for producing a stable free radical by burningoff the halogen or producing a catalyst by burning off the halogen andadding chromium or other catalytic material.

The production of free radical-containing silica by gamma irradiation isknown but this causes other degradation of the silica. The production ofa small amount of free radicals in silica by mechanically grinding isalso known but such a composition exhibits only a small amount of freeradicals and is physically broken down. The instant invention gives anon-degraded (by either electromagnetic irradiation or physicalgrinding) silica, containing a strong presence of free radicals, i.e., ag value of 1.8 to 2.2, for instance.

In the third embodiment wherein a sulfur-containing material isutilized, it is preferred that there be present sulfur, oxygen andcarbon. Accordingly, mixtures of a sulfur-containing compound, such ascarbon disulfide, and an oxygen-containing compound, such as acarboxylic acid or an alcohol, can be used. Most preferred is carbonylsulfide since it contains both oxygen, sulfur and in addition carbon.Other exemplary sulfur-containing compounds include carbon monosulfide,carbon subsulfide, methanethiol, 2-methyl-1-propanethiol, eicosanethiol,benzenethiol, para-benzenedithiol, thiophene, thiophene-2-thiol,1,2,3-propanetrithiol, dimethylsulfide, diethylsulfide, diphenylsulfide,benzylphenylsulfide, didimethylsulfide, di-4-tolyldisulfide,2,2'-dinaphthyl disulfide, diethyltrisulfide, and the like. Generally, aweight ratio of supported catalyst to organic sulfur compound rangingfrom about 100:1 to about 0.1:1, more preferably from about 20:1 to 2:1have been found suitable for this purpose. Since the chromium is arelatively small part of the total catalyst, the weight ratio of thesilica containing material to the sulfur-containing compound isessentially the same, i.e., from about 100:1 to about 0.1:1 morepreferably from about 20:1 to 2:1.

The sulfur-containing material can be used alone or diluted with aninert gas such as nitrogen, argon or helium. If so diluted, thesulfur-containing material will generally constitute 1-90 mole percentof the mixture.

Suitable alcohols for use in conjuction with the sulfur-containingmaterials include saturated and unsaturated aliphatic and aromaticalcohols with boiling points of about 300° C. or less as a matter ofconvenience. Particularly preferred alcohols from an economic standpointand ready availability are methanol and isopropanol.

Suitable carboxylic acids for this purpose include saturated andunsaturated compounds which are normally liquid as a matter ofconvenience. A fatty acid, particularly acetic acid, is presentlypreferred because of ready availability and low cost.

The alcohol or acid if used can be used in an amount so as to give amole ratio of the sulfur-containing material to the alcohol or acidwithin the range 0.1:1 to 10:1.

These treatments are carried out at a temperature within the range of500°-1000° C., pr,eferably 750°-925° C. The time for this treatment isat least 5 minutes, preferably 20 minutes to 10 hours, more preferably 2to 8 hours. Shorter times, of course, are generally employed at thehigher temperatures and longer times at the lower temperatures. Two to 8hours are especially preferred times for reduction temperatures in therange of 750°-925° C., for instance. With elemental iodine plus CO whichis preferred, temperatures of 700°-950° C., preferably 750°-925° C. andtimes of 1 to 4 hours are particularly preferred. About 800° C. appearsto be optimum. The term "reduction" is used since the treating agentsare reducing agents although the silica is not believed to be reduced inthe normal sense of the word, i.e., the treatment is carried out underreducing conditions.

After the treatment, if the agent is a bromine- or iodine-containingmaterial employed in the presence of CO, a surface bromide or iodidecompound is formed and it is essential or at least highly preferred thatthe material be given a treatment in air or other oxygen-containingambient to burn off surface bromide or iodide if it is to be impregnatedwith chromium to form a catalyst. With the CO or sulfur treatment, thisoxidizing treatment is preferred but not essential since a similarsurface compound is not formed. This oxidizing treatment is carried outby simply heating the bromine- or iodine-treated support in a dryoxygen-containing ambient, for instance, air at a temperature rangingfrom about 300°-1000° C., preferably about 525°-925° C., for a timeranging from 10 minutes to 10 hours, more preferably from 1 to 5 hours.Bromine gas is released from the catalyst during this step, and isreplaced by oxide groups, leaving an improved catalyst support in thoseinstances where a bromine component is used under conditions to givebound bromine. Similarly, iodine is given off from supports similarlytreated with iodine during that treatment to burn off the iodine. Butiodine, like bromine is not given off by heating at 871° C. in CO or N₂.

The support after the reducing treatment and the subsequent oxidation,if employed is then cooled and the chromium added without theintroduction of water. Suitable chromium compounds are selected fromdiarene chromium compounds as described in Delap, U.S. Pat. No.3,976,632 (Dec. 4, 1974), the disclosure of which is hereby incorporatedby reference; alkyl or aryl esters of chromic acid and chromiumacetylacetonate as described in Hill, U.S. Pat. No. 3,349,067 (Oct. 24,1967), the disclosure of which is hereby incorporated by reference.Bis(cyclopentadienyl)chromium(II) compounds as described in Karpinka,U.S. Pat. No. 3,709,853 (Jan. 9, 1973), the disclosure of which ishereby incorporated by reference and silyl chromates as described inJohnson, U.S. Pat. No. 3,704,287 (Nov. 28, 1972), the disclosure ofwhich is hereby incorporated by reference. Generally, a solution or aslurry of the chromium compound in a dry organic liquid inert to thecompound and support is used to contact the treated support. Examples ofsuitable organic liquids include paraffins such as n-heptane,cycloparaffins such as cyclohexane and aromatic hydrocarbons such asbenzene. Following the contacting, the composite is dried. Sufficientchromium is used to give 0.001 to 10, preferably 0.1 to 5, morepreferably 0.5 to 1 weight percent based on the weight of thesilica-containing base.

The composite after incorporation of the chromium compound is thenactivated in a manner conventional in the art for the particular type ofchromium compound used. Preferably, the composite is activated bycontact with an oxygen-containing ambient such as air at temperaturesranging from about 15°-870° C., preferably 315°-760° C., more preferably300°-400° C. for sulfur-treated supports, 300°-500° C. for bromine- oriodine-treated supports, and 400°-600° C. for CO-treated supports. Asnoted, the preferred ambient is air. However, any oxygen-containingambient having from 2-100% oxygen and from 0-98% of an inert gas such asnitrogen can be used. In some instances, it is desirable to use acontrolled smaller amount of oxygen by utilizing a nitrogen-air mixture.It is also possible, though much less preferred, to activate theπ-bonded organochromium compounds, particularly the dicyclopentadienylchromium(II) compounds in an inert atmosphere such as nitrogen for thesame times and temperatures used with oxygen. Following the activation,the catalysts are cooled, if necessary, and stored in a dry, inertatmosphere until ready for use. NO₂, N₂ O and oxygen-containing halogencompounds can also be used as the oxidizing agent. Suitableoxygen-containing halogen compounds are I₂ O₅ and Cl₂ O.

The activation times will generally be at least 5 minutes, preferably 10minutes to 10 hours, more preferably 30 minutes to 3 hours. Theconcentration of the chromium compound is such that the final activatedcatalyst contains from 0.001 to 10 preferably 0.1 to 5, more preferablyabout 1 weight percent chromium based on the weight of the chromiumcompound and support.

The catalysts of this invention can be used to polymerize at least onemono-1-olefin containing 2 to 8 carbon atoms per molecule. The inventionis of particular applicability in producing ethylene homopolymers andcopolymers from mixtures of ethylene and 1 or more comonomers selectedfrom 1-olefins or dienes containing 3 to 8 carbon atoms per molecule.Exemplary comonomers include aliphatic 1-olefins, such as propylene,1-butene, 1-hexene, and the like and conjugated or non-conjugateddiolefins, such as 1,3-butadiene, isoprene, piperylene,2,3-dimethyl-1,3-butadiene, 1,4-pentadiene, 1,7-hexadiene, and the likeand mixtures thereof. Ethylene copolymers preferably constitute about90, preferably 95 to 99 mole percent polymerized ethylene units. Mostpreferred monomers are at least one of ethylene, propylene, 1-butene,and 1-hexene.

The polymers can be prepared from the activated catalysts of thisinvention by solution polymerization, slurry polymerization, and gasphase polymerization techniques using conventional equipment andcontacting processes. However, the catalysts of this invention areparticularly suitable in slurry polymerizations for the production ofhigh melt index (MI) polymers, i.e., polymers having MI values in the 1to 15 range and above at 102° C. polymerization temperature in theabsence of molecular weight modifiers, such as hydrogen, and molecularweight distribution value sufficiently narrow to be of commercialinterest for applications such as injection molding. For example,ethylene homopolymers exhibiting a melt index in the 1 to 15 range canbe obtained by contact with the catalyst of this invention, whereasotherwise identical catalyst using a base conventionally prepared yieldfractional MI polymers, i.e., polymer of a MI of less than 1 at areactor temperature of 102° C. At higher reactor temperatures, higher MIand lower HLMI ratio values are obtained. Thus, for a comparison betweena control run and an invention run to be valid they must be at the samepolymerization temperature. At a reactor temperature of 110° C.,polymers of 15 to 35 MI and higher can be produced as compared withpolymers of 5 to 6 maximum MI without the treatment of the support setout in this invention. The high MI polymers made at 110° C. reactortemperature have HLMI/MI (high load MI/regular MI) values ranging fromabout 33 to 38 with M_(w) /M_(n) ratios of about 4. M_(w) is weightaverage molecular weight, M_(n) is number average molecular weight;these values can be determined by means of GPC. Such resins can beinjection molded in conventional apparatus to form tough, low warpagearticles.

As can be seen, in order for a fair comparison to be made, it must bedone between an invention run and a control run carried out at the samepolymerization temperature. Higher melt flow and better molecular weightdistribution as evidenced by lower HLMI/MI ratios are obtained at thehigher temperatures. However, as is noted hereinabove, there is apractical limit to the maximum temperature which can be utilized in aparticle-form process. The runs herein were carried out at a relativelylow temperature simply because of the greater ease of measuring the meltindex values at the lower levels. Actually, polymerization is generallycarried out in conventional systems at the highest temperature possiblewithout putting the polymer into solution so as to get the highestpossible melt index. However, with this invention, polymerization atthis temperature produced such high melt index polymer that it wasdifficult to measure and hence lower polymerization temperatures weregenerally used.

Particle form polymerizations are carried out in an inert diluent suchas a paraffin, aromatic or cycloparaffin hydrocarbon at a temperaturewhere the resulting polymer is insoluble. For predominantly ethylenepolymer, the particle form process is carried out at a temperature of66°-110° C.

The catalysts of this invention can be used with conventionalcocatalysts if desired. Also, hydrogen can be used to further increasethe MI if desired.

EXAMPLE 1 (Embodiment 1)

Samples of a dried, coprecipitated silica-titania cogel prepared asdescribed in said U.S. Pat. No. 3,887,494, were heated in a fluidizedbed quartz activator in an atmosphere of either pure, dry carbonmonoxide or dry air for 4 hours at 1600° F. (870° C.). Gas flow rate was42 liters per hour in each instance. Following this treatment,individual portions of the CO-treated support and the air-treatedsupport were impregnated with a 1 weight percent solution of dicumenechromium n-hexane sufficient to obtain composites each containing either0.5 or 1 weight percent of the chromium compound calculated as chromium,based on the dry weight of support plus chromium compound. Severalcatalyst samples were also prepared by impregnation of the CO-treatedsupport as described above with a 1 weight percent solution of t-butylchromate in n-hexane sufficient to provide 0.5 weight percent chromiumon a dry basis. Each composite was dried to remove solvent and each wascharged to the activator, unless otherwise indicated, under specifiedtemperatures for 2 hours for activation. Samples of each recoveredcatalyst were used in the particle form polymerization of ethylene at215° F. (102° C.).

The treating conditions employed and polymer melt index (MI) valuesobtained are presented in Table I. A column is also included for theratio of high load melt index/melt index (HLMI/MI) determined for eachpolymer. The ratios are related to molecular weight distribution of thepolymer, the smaller the number, the narrower the molecular weightdistribution. Each MI value is adjusted for a productivity value of 5000g polymer/g catalyst to give a true basis for comparing results.

                  TABLE I                                                         ______________________________________                                        Effect Of Support Pretreatment According To                                   Embodiment 1 On Polymer Melt Index                                                  Support                                                                       Pre-     Wt. %     2 Hour Air                                           Run.sup.(1)                                                                         treatment                                                                              Chromium  Activation                                                                             Polymer                                     No.   Ambient  In Catalyst                                                                             °F.                                                                         °C.                                                                          MI   HLMI/MI                              ______________________________________                                        1.sup.(2)                                                                           air      0.5        80   27   0.74 42                                   2     air      0.5        600 316   0.74 61                                   2a    CO       0.5        600 316   1.5  54                                   3     air      0.5        800 427   0.88 58                                   3a    CO       0.5        800 427   2.2  58                                   4a    CO       0.5        900 482   2.9  50                                   5     air      0.5       1000 538   1.2  51                                   5a    CO       0.5       1000 538   2.8  55                                   6     air      0.5       1200 649   0.87 61                                   6a    CO       0.5       1200 649   3.1  55                                   7a    CO       0.5       1300 704   1.8  52                                   8     air      0.5       1400 760   0.55 67                                   8a    CO       0.5       1400 760   1.2  57                                   9     air      0.05      1600 871   0.56 78                                   9a    CO       0.5       1600 871   0.89 61                                   10a.sup.(3)                                                                         CO       0.5        800 427   2.1  54                                   11a.sup.(3)                                                                         CO       0.5       1000 538   2.7  49                                   12.sup.(3)                                                                          air      1          600 316   1.3.sup.(4)                                                                        84                                   12a   CO       1          600 316   4.6  67                                   ______________________________________                                         Notes:                                                                        .sup.(1) All runs with subscript a are invention runs.                        .sup.(2) Catalyst was treated with 0.5 mole oxygen per mole chromium at       80° F. for activation.                                                 .sup.(3) Chromium compound used in preparing catalyst in runs 10a, 11a an     12 was tbutyl chromate. All other catalysts made with dicumene chromium.      .sup.(4) Reactor temperature employed was 212° F. All other runs       employed 215° F.                                                  

The runs in Table I have been grouped to show how the supportpretreatment conditions employed affect the melt index of polyethyleneproduced with catalysts prepared from the treated supports and activatedunder the same conditions. Thus, control run 2 shall be compared withinvention run 2a, control run 3 with invention run 3a, and the like. Incomparing those runs, it can be seen that pretreating the support incarbon monoxide has a beneficial effect on the melt index capability ofcatalyst prepared from such support. Thus, the melt index capability hasincreased from about 1.6-fold in runs 9 vs. 9a up to about 3.6-fold inruns 6 vs. 6a in which near optimum conditions appear to be realized. Acomparison of runs 3a with 10a and 5a with 11a show that catalystsprepared with dicumene chromium and t-butyl chromate are substantiallyequivalent in performance based on the melt index values of the polymersmade with the catalysts. However, the HLMI/MI values of the polymers aresomewhat higher with catalysts prepared with dicumene chromium ratherthan with t-butyl chromate. This suggests that somewhat broadermolecular weight distribution polymer may be made with catalystsprepared with diarene chromium compounds in comparison to those madewith chromic acid esters.

The effect of increasing the amount of chromium from 0.5 weight percentto 1 weight percent on catalysts otherwise identical in preparation isillustrated in runs 2a and 12a, respectively. Thus, in this instance,doubling the chromium concentration resulted in about a 3-fold increasein polymer melt index.

EXAMPLE 2 (Embodiment 2)

Another series of catalysts was prepared from samples of the cogelsupport of Example 1 which were separately pretreated in variousambients in the fluidized bed activator used before. After thepretreatment, each support was cooled, recovered and impregnated with a1% solution of dicumene chromium in n-hexane sufficient to give 0.5weight percent chromium based on the dry weight of the composite. Eachsample after drying was reheated in the activator for 2 hours at 600° F.in dry air, cooled, recovered and stored in a dry inert atmosphere untilready for use. As in Example 1, the flow rate of gas in the activatoremployed was 42 liters per hour in each run.

Ethylene was polymerized under particle form conditions employing areactor temperature of 215° F. (102° C.).

The pretreating conditions employed and polymer MI and HLMI/MI resultsobtained are given in Table II.

                  TABLE II                                                        ______________________________________                                        Effect Of Halogenated Support Pretreatment                                    According to Embodiment 2                                                     Support Pretreatment                                                                      Am-     Polymer                                                    No.Run                                                                               1Ambient                                                                              °C.                                                                            2bient                                                                            °C.                                                                         MI                                                                                 ##STR1##                                                                             Remarks                          ______________________________________                                        1.sup.(1)                                                                          air       871    --   --   0.75 61     control                           2.sup.(2)                                                                          CO        871    --   --   1.5  54     (Embodi-                                                                      ment 1)                           3.sup.(3)                                                                          CO + Br.sub.2                                                                           649    N.sub.2,                                                                           871  3.9  80     (Embodi-                                                air                   ment 2)                           4.sup.(4)                                                                          CO + Br.sub.2                                                                           871    air  871  11.5 56     (Embodi-                                                                      ment 2)                           5    air + Br.sub.2                                                                          871    --   --   1.7  73     (Embodi-                                                                      ment 2)                           6.sup.(5)                                                                          air + CCl.sub.4                                                                         871    --   --    --  --     dead                                                                          catalyst                          7    CO + Br.sub.2                                                                           871    --   --   0.1  71     almost                                                                        dead                              ______________________________________                                         Notes:                                                                        All supports were brought up to 871° C. in dry air before treating     with the other ambients. The air was purged with nitrogen before admittin     CO to the activator in runs 2-4.                                              .sup.(1) Support was heated for 4 hours in air at 871° C.              .sup.(2) Support was heated for 4 hours in CO at 871° C.               .sup.(3) After contact with the bromineCO mixture at 649° C., the      temperature was raised to 871° C. while switching to nitrogen and      held for 2 hours in nitrogen at 871° C. Then the nitrogen was          replaced with dry air and the support heated in air for 2 hours at            871° C.                                                                .sup.(4) After contact with the bromineCO mixture at 871° C., the      support was heated in pure CO for 1 hour at 871° C., the CO flushe     out with N.sub.2 then the support was heated in air at 871° C. for     2 hours.                                                                      .sup.(5) Weight ratio of support to CCl.sub.4 was about 14:1. Since           CCl.sub.4 decomposes to Cl.sub.2 + C under the conditions employed, a         calculated weight ratio of support to Cl.sub.2 was about 15:1 in this run                                                                              

Inspection of the results in Table II show in runs 2, 3 and 4 thatpretreating the support in a mixture of CO and bromine which is thentreated with air and finally converted into catalyst improves the meltindex capability of that catalyst beyond that resulting from a COpretreatment alone. In addition, runs 2 and 5 demonstrate thatpretreating the support in a mixture of air and bromine is aboutequivalent to pretreating it in CO based on the melt index capability ofcatalysts prepared from the thus treated supports.

Analysis has shown that a surface bromide is formed when the support isbromine treated at high temperature. This bromide complex is itselfinjurious to the polymerization process, as in run 7. However, when thesurface bromide is burned off by a high temperature air treatment (runs3--4--5), Br₂ gas can be seen leaving the catalyst and the final resultis a greatly improved polymerization catalyst support.

EXAMPLE 3 (Embodiment 2)

A cogel similar to that used in Examples 1 and 2 containing 2 weightpercent titanium was heated in nitrogen to 871° C. It was then treatedwith HBr for 1/2 hour at 871° C. and then in air at 871° C. for 1/2hour, then nitrogen for 31/2 hours at 871° C., and then air for 1 hourat 871° C. and cooled to room temperature. It was then impregnated withchromium as in the previous examples and oxidized in air for 2 hours at648° C. Polymerization runs were carried out as before at 107° C. Theresulting ethylene polymer had a melt index of 15, HLMI/MI ratio of 34and a productivity of 5590 g polymer/g catalyst. The induction time was15 minutes and the run time 31 minutes. In a control run, the same typeof cogel without the HBr treatment was treated with chromium acetate togive 1 percent chromium and activated in air at 871° C. for 5 hours. Onpolymerization of ethylene under the same conditions as above, theresulting polymer had a melt index of 2.8 and a HLMI/MI ratio of 50, anda productivity of 5620 g polymer/g catalyst and an induction time of 25minutes and a run time of 75 minutes.

This shows better than a fivefold increase in melt index and a drasticlowering of the HLMI/MI ratio utilizing the treatment of the support setout herein. In both the invention run and the control run, theactivation of the catalyst and the subsequent polymerization conditionswere identical and conventional, the entire improvement beingattributable to the pretreatment of the base prior to incorporation ofthe chromium.

EXAMPLE 4 (Embodiment 2)

A sample of 10.6 grams of silica-titania cogel containing about 2 weightpercent titanium and no chromium was heated in air to 871° C., held incarbon monoxide at 871° C. for 2 hours, and thereafter 1/2 cc brominewas injected. The catalyst was reoxidized in air at 316° C. for 1 hour.The catalyst was found to contain 3.3 weight percent bromine based onthe weight of the cogel. In another example, the catalyst was found tocontain 8.3 weight percent bromine based on the weight of the cogel.When these catalysts were treated with air at 871° C., Br₂ could be seenleaving the silica and analysis showed the catalyst to contain nobromine. When Br₂ was injected into an air atmosphere in presence of thesupport, no bromine was found on the catalyst. The bromine does not comeoff at 871° C. in carbon monoxide or nitrogen.

EXAMPLE 5 (Embodiment 2)

Cogel similar to that of Example 3 and containing 2 weight percenttitanium was heated in air to 871° C. and then held in nitrogen at 871°C. for 2 minutes. It was then treated with a gas mixture containing I₂and CO at 871° C. for 2 hours and then nitrogen for 2 minutes and thenin air at 871° C. for 1 hour, and then cooled to room temperature. Itwas then impregnated with chromium as in the previous examples (0.5weight percent Cr) and oxidized in air for 1 hour at 316° C.Polymerization runs were carried out as before at 102° C. This isinvention Run A. In Run B, the same procedure was followed except no I₂was used. In Run C, the same procedure of Run A was used except the airtreatment after the I₂ treatment was omitted. The results were asfollows:

    ______________________________________                                        Run              A         B       C                                          ______________________________________                                        I.sub.2 treatment                                                                              Yes       No      Yes                                        Air treatment befor Cr added                                                                   Yes       Yes     No                                         MI               7.21      2.83    1.16                                       HLMI/MI Ratio    55        53      69                                         Run Time, min.   37        58      45                                         Productivity g/g 4930      5212    5610                                       ______________________________________                                    

A comparison of Runs A and B shows that a further improvement over thatobtained by using CO (Run B) is obtained by also using I₂ (Run A). Run Cshows that in order to fully achieve this advantage the treated silicamust be given an oxidation treatment to remove halogen.

EXAMPLE 6 (Embodiment 2)

Thirty grams of a sample of 952 Grade silica commercially available fromDavison Chemical Company having a surface area of 250 sq m/g was heatedin air to the desired temperature and held there for 3 hours. Then about15 g of I₂ was vaporized into CO and passed through this silica over aperiod of 2-3 hours. The silica was then cooled to room temperature andanalyzed chemically for iodine with the following results.

    ______________________________________                                        Treatment Temperature, °C.                                                               Millimoles I/g Silica                                       ______________________________________                                        500               0.02                                                        650               0.02                                                        700               0.15                                                        800               0.31                                                        900               0.09                                                        ______________________________________                                    

In a second series identical to that above except 2 g I₂ instead of 15were used, the results were:

    ______________________________________                                        Treatment Temperature, °C.                                                               Millimoles I/g Silica                                       ______________________________________                                        300               0.00                                                        500               0.01                                                        600               0.03                                                        800               0.17                                                        900               0.16                                                        ______________________________________                                    

In a third series identical to the first except that Cab-O-Sil S-17grade silica was used instead of Davison 952, the results were asfollows:

    ______________________________________                                        Treatment Temperature, °C.                                                               Millimoles I/g Silica                                       ______________________________________                                        800               0.51                                                        ______________________________________                                    

In a fourth series identical to the first, the results were:

    ______________________________________                                        Treatment Temperature, °C.                                                               Millimoles I/g Silica                                       ______________________________________                                        750               0.22                                                        ______________________________________                                    

This silica was heated in air to 750° C. and the color changed from grayto yellow. It gave off a purple gas. Analysis after this burning offtreatment showed 0.06 millimoles of I/g silica. In a fifth seriesidentical to the first except that COS was used in place of CO, theresults were as follows:

    ______________________________________                                        Treatment Temperature, °C.                                                               Millimoles I/g Silica                                       ______________________________________                                        800               0.22                                                        ______________________________________                                    

EXAMPLE 7 (Embodiment 2)

The iodinated silica of Example 6 having 0.22 millimoles of iodine pergram silica was used to pack a chromatographic column about 8millimeters in diameter and 21/2 inches long. Helium was the carrier gasand the column was held at 25° C. Various compounds were injected intothe column and retention times were measured.

    ______________________________________                                        Compound         Retention Time                                               ______________________________________                                        air               .72 min.                                                    ethylene          .80 min.                                                    isobutane        1.35 min.                                                    pentane          2.40 min.                                                    hexane           >10 min.                                                     heptane          >30 min.                                                     CCl.sub.4        6.60 min.                                                    acetone          1 day estimated visually                                     ______________________________________                                    

In a separate run, isobutane was separated from pentane using the abovedescribed column.

EXAMPLE 8 (Embodiment 2)

A portion of the iodinated silica of Example 7 was oxidized in air at300° C. for one hour, which released I₂ gas initially. A 61/2 inchchromatographic column was made, and the following retention times wereobtained at 25° C.

    ______________________________________                                        Compound         Retention Time                                               ______________________________________                                        air              .70     min.                                                 ethylene         .75     min.                                                 isobutane        .75-.76 min.                                                 n-butane         .90-.94 min.                                                 pentane          1.34    min.                                                 hexane           2.55    min.                                                 heptane          4.3     min. (broad)                                         ______________________________________                                    

Even though this column was twice as long as the column used in Example7 with the iodinated silica, the retention times for most compounds areconsiderably less. This shows a different attraction for the silica, andfurther shows the difference between the two materials. It is ofparticular note that this column was effective in separating isobutanefrom normal butane as evidenced by the different retention times whereasthe iodinated silica did not.

EXAMPLE 9 (Embodiment 3)

Silica-titania cogel containing about 2 percent titanium was treatedwith carbonyl sulfide. In some instances, the support was thenreoxidized and in other instances it was not. Thereafter, the supportwas impregnated with a dry hexane solution of dicumene chromium to giveabout 0.5 weight percent chromium based on the weight of the cogel. Theresults are shown hereinbelow in Table III.

                                      TABLE III                                   __________________________________________________________________________    Sulfur Treatment of Cogel Support                                              No.Run                                                                           Support Pretreatment                                                                      ReoxidationSupport                                                                   ReoxidationFinal                                                                     Color  Temp.Run                                                                          MI                                                                               ##STR2##                                                                            TimeRun                                                                          Prod.                    __________________________________________________________________________    1  15% COS/870° C./1 hr.                                                              None   315° C./1 hr.                                                                 Orange Tan                                                                           102° C.                                                                    55 42.3  34 5700                      2  15% COS/870° C./1 hr.                                                              None   480° C./1 hr.                                                                 Orange 107° C.                                                                    65 37.5  33 5060                      3  15% COS/870° C./1 hr.                                                              540° C./1 hr.                                                                 315° C./1 hr.                                                                 Orange Tan                                                                           102° C.                                                                    87 --    30 4460                      4  15% COS/870° C./1 hr.                                                              540° C./1 hr.                                                                 480° C./1 hr.                                                                 Orange 102° C.                                                                    27 46.1  27 6350                      5  15% COS/870° C./1 hr.                                                              540° C./1 hr.                                                                 650° C./1 hr.                                                                 Orange 102° C.                                                                    9.7                                                                              50.7  34 5160                      6  15% COS/870° C./1 hr.                                                              870° C./1 hr.                                                                 315° C./1 hr.                                                                 Orange Tan                                                                           102° C.                                                                    84 --    41 5160                      7  15% COS/870° C./1 hr.                                                              870° C./1 hr.                                                                 480° C./1 hr.                                                                 Orange 102° C.                                                                    19.2                                                                             50.0  32 5120                      8  15% COS/870° C./1 hr.                                                              870° C./1 hr.                                                                 650° C./1 hr.                                                                 Orange 102° C.                                                                    12.5                                                                             .[.29.7.]..Iadd.39.7.Iaddend.                                                       33 4590                      __________________________________________________________________________

As control runs, cogel base with no chromium was calcined in air at 870°C. for 4 hours, then impregnated with 0.5 weight percent chromium asdicumene chromium in hexane. The catalysts were then reoxidized asindicated hereinbelow in Table IV for 2 hours in air. The results areshown hereinbelow.

                  TABLE IV                                                        ______________________________________                                        Anhydrous Promotion of Air Activated Cogel Base                                No.Run                                                                             Temp.Reoxidation                                                                        Color      MI                                                                                 ##STR3##                                                                             TimeRun                                                                            Prod.                             ______________________________________                                        1     25° C.                                                                          yellow green                                                                             no go                                               2     25° C..sup.(A)                                                                  green      0.74 42     146  5500                               3    160° C.                                                                          olive      no go                                               4    315° C.                                                                          orange     0.74 61     53   4810                               5    315° C..sup.(B)                                                                  orange     1.3  46     70   5210                               6    425° C.                                                                          orange     0.88 58     45   5030                               7    540° C.                                                                          orange     1.2  51     40   5470                               8    650° C.                                                                          orange     0.87 61     42   4870                               9    760° C.                                                                          orange     0.55 67     33   4970                               10   870° C.                                                                          orange     0.56 78     40   5430                               ______________________________________                                    

Polymerization was done at 102° C. and 550 psig ethylene. All MI valueshave been corrected to 5000 gm/gm productivity.

(A) 0.5 mole O₂ /mole Cr injected into a N₂ stream.

(B) Run at 105° C.

As can be seen, much improved melt index values are obtained utilizingthe invention as set out in the data from Table III. Indeed, theimprovement for embodiment 3 is not only greater than the control runsfrom Table IV but also superior to the results as shown in embodiments 1and 2. As can be seen, melt index values ranging from 0.5 to 1.2 areobtained with the control compared with values ranging from 1.2 to 11.5for embodiments 1 and 2; however, values ranging up to 87 are obtainedwith embodiment 3.

In embodiment 3, the preferred reoxidation temperature is lower than thepreferred temperature in embodiments 1 and 2.

In comparing runs 1, 3 and 6 of Table III, each catalyst beingreoxidized at 315° C. for 1 hour, it is seen that melt index potentialof the catalyst is increased by reoxidizing the treated support at anelevated temperature, i.e., 540° to 870° C., prior to impregnation withthe Cr compound. On the other hand, the preferred reoxidationtemperature employed for the catalyst is about 315° C. As the finalreoxidation temperature exceeded 315° C., the melt index of polymerproduced with that catalyst decreased, i.e., 87 for run 3 at 315° C., 27for run 4 at 480° C. and 9.7 for run 5 at 650° C. (Run 2 is higher thanrun 1 because it is the only one run at a higher reactor temperature).

Unlike in the bromine or iodine treatment, analysis of the sulfurtreated catalyst bases shows that no sulfur is left behind on thesupport. That is, immediately after the treatment with, say carbonylsulfide, the material can be cooled and analyzed and no sulfur is foundon the support.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

We claim:
 1. A polymerization process comprising contacting at least onemono-1-olefin having 2 to 8 carbon atoms with a catalyst prepared bysubjecting a silica-containing support at an elevated temperature to atreating ambient selected from (1) .[.carbon monoxide, (2).]. ahalogen-containing component selected from bromine, iodine, HBr, HI,organic bromides, and organic iodides, which halogen-containingcomponent also either contains air or is followed by air or .[.(3).]..Iadd.(2) .Iaddend.a carbon, oxygen and sulfur-containing composition,thereafter incorporating a chromium compound under anhydrous conditionsto thus form said catalyst and thereafter activating said catalyst in anoxygen ambient.
 2. A polymerization process according to claim 1 whereinsaid olefin comprises ethylene.
 3. A polymerization process according toclaim 1 wherein said at least one mono-1-olefin is selected fromethylene, propylene, and 1-butene.
 4. A polymerization process accordingto claim 1 wherein said polymerization conditions comprise a temperatureof 66°-110° C.
 5. A method according to claim 1 wherein after saidincorporation of said chromium compound said catalyst is activated in anoxygen ambient at a temperature within the range of 15°-870° C. for atime of at least 5 minutes.
 6. A method according to claim 1 whereinsaid silica is a coprecipitated silica-titania cogel.
 7. A methodaccording to claim 1 wherein said chromium is incorporated in an amountsufficient to give 0.1 to 5 weight percent chromium based on the weightof said support.
 8. A method according to claim 1 wherein said supportis a silica-titania cogel containing 0.5 to 5 weight percent titaniumbased on the weight of said cogel. .[.
 9. A method according to claim 8wherein said treating ambient is carbon monoxide..].
 10. A methodaccording to claim 8 wherein said treating ambient is bromine vapor. 11.A method according to claim 8 wherein said treating ambient is HBr. 12.A method according to claim 8 wherein said treating ambient isbromine+air.
 13. A method according to claim 8 wherein said treatingambient is iodine vapor.
 14. A method according to claim 8 wherein saidtreating ambient is HI.
 15. A method according to claim 8 wherein saidtreating ambient is iodine+air.
 16. A method according to claim 8wherein said treating ambient is said halogen containing component of.[.(2).]. .Iadd.(1) .Iaddend.and wherein said halogen-containingcomponent is bromine and wherein said ambient contains in additioncarbon monoxide.
 17. A method according to claim 8 wherein said treatingambient is said halogen-containing component of .[.(2).]. .Iadd.(1).Iaddend.and wherein said halogen-containing component is iodine andwherein said ambient contains in addition carbon monoxide.
 18. A methodaccording to claim 8 wherein said treating ambient is carbonyl sulfide.19. A method according to claim 8 wherein said elevated temperature iswithin the range of 759°-925° C.
 20. A method according to claim 1wherein said chromium compound is incorporated by means of an inertliquid hydrocarbon diluent or solvent.
 21. A method according to claim20 wherein said chromium compound is one of a π-bonded organochromiumcompound, esters of chromic acid, and chromium acetylacetonate.
 22. Amethod according to claim 1 wherein said support is preoxidized by beingsubjected to oxidation conditions after being subjected to said ambientand prior to incorporation of said chromium compound.
 23. A methodaccording to claim 22 wherein said support is a silica-titania cogelcontaining about 2 weight percent titanium, said elevated temperature iswithin the range of 750°-925° C., said chromium compound is selectedfrom tertiary butyl chromate, and dicumene chromium carried in normalhexane, and wherein said preoxidation is carried out at a temperaturewithin the range of 525°-925° C., and wherein after said incorporationof said chromium compound said catalyst is activated by heating in airat a temperature within the range of 315°-760° C. .Iadd.
 24. Apolymerization process comprising contacting at least one mono-1-olefinhaving 2 to 8 carbon atoms with a catalyst prepared by subjecting asilica-titania cogel support at an elevated temperature to a treatingambient comprising carbon monoxide, thereafter incorporating a chromiumcompound under anhydrous conditions to thus form said catalyst andthereafter activating said catalyst in an oxygen ambient..Iaddend..Iadd.
 25. A polymerization process comprising contacting atleast one mono-1-olefin having 2 to 8 carbon atoms with a catalystprepared by subjecting a silica-containing support at an elevatedtemperature to a treating ambient comprising carbon monoxide to producea treated support, thereafter preoxidizing said treated support bysubjecting said treated support to oxidation conditions, thereafterincorporating a chromium compound under anhydrous conditions to formsaid catalyst and thereafter activating said catalyst in an oxygenambient. .Iaddend.